Industrial controllers are special purpose processing devices used for controlling industrial processes, machines, manufacturing equipment, and other factory automation applications. In accordance with a control program or routine, an industrial controller can measure one or more process variables or inputs representative of the status of a controlled process, and change outputs effecting control of the process. The inputs and outputs can be binary, (e.g., on or off), and/or analog assuming a continuous range of values. The control routine can be executed in a series of execution cycles with batch processing capabilities, and can comprise one or more functional units. Such a control routine can be created in a controller configuration system having tools and interfaces whereby a user can implement a control strategy using programming languages or graphical representations of control functionality. The control routine can be downloaded from the configuration system into one or more controllers for implementation of the control strategy in controlling a process or machine.
The measured inputs received from a controlled process and the outputs transmitted to the process can pass through one or more input/output (I/O) modules in a control system, which serve as an electrical interface between the controller and the controlled process, and can be located proximate or remote from the controller. The inputs and outputs can be recorded in an I/O table in processor memory. Input values can be asynchronously read from the controlled process by one or more input modules and output values can be written directly to the I/O table by a processor for subsequent communication to the process by specialized communications circuitry. An output module can interface directly with a controlled process, by providing an output from an I/O table to an actuator such as a motor, drive, valve, solenoid, and the like.
During execution of the control routine, values of the inputs and outputs exchanged with the controlled process pass through the I/O table. The values of inputs in the I/O table can be asynchronously updated from the controlled process by dedicated scanning circuitry. This scanning circuitry can communicate with input and/or output modules over a bus on a backplane or network communications. The scanning circuitry can also asynchronously write values of the outputs in the I/O table to the controlled process. The output values from the I/O table can be communicated to one or more output modules for interfacing with the process. Thus, a controller processor can simply access the I/O table rather than needing to communicate directly with the controlled process.
In distributed control systems, controller hardware configuration can be facilitated by separating the industrial controller into a number of control modules, each of which performs a different function. Particular control modules needed for the control task can then be connected together on a common backplane within a rack and/or through a network or other communications medium. The control modules can include processors, power supplies, network communication modules, and I/O modules exchanging input and output signals directly with the controlled process. Data can be exchanged between modules using a backplane communications bus, which can be serial or parallel, or via a network. In addition to performing I/O operations based solely on network communications, smart modules exist which can execute autonomous logical or other control programs or routines.
Various control modules of a distributed industrial control system can be spatially distributed along a common communication link in several racks. Certain I/O modules can thus be located proximate a portion of the control equipment, and away from the remainder of the controller. Data can be communicated with these remote modules over a common communication link, or network, wherein all modules on the network communicate via a standard communications protocol.
In a typical distributed control system, one or more I/O modules are provided for interfacing with a process. The outputs derive their control or output values in the form of a message from a master or peer device over a network or a backplane. For example, an output module can receive an output value from a processor, such as a programmable logic controller (PLC), via a communications network or a backplane communications bus. The desired output value is generally sent to the output module in a message, such as an I/O message. The output module receiving such a message will provide a corresponding output (analog or digital) to the controlled process. Input modules measure a value of a process variable and report the input values to a master or peer device over a network or backplane. The input values can be used by a processor (e.g., a PLC) for performing control computations.
In such control systems, data can be collected, analyzed and disbursed throughout a control architecture. In some instances, data related to a particular system and/or process can be conveyed to a user to inspect desired data values. Further, data can relate to multiple aspects of a particular process and can be channeled to a particular destination utilizing a number of means. Conventionally, data transmitted throughout a control architecture is sent to various requesters without regard to the effect of the overall performance of the network. In addition, the data can be delivered to a particular requestor wherein the data cannot be employed and/or the data must be first channeled through a middleware application to insure the data can be employed by the requesting application. Thus, what is needed is a technique to effectively locate and employ data throughout a control architecture.